The present invention relates to a method and an apparatus for protecting buildings against windstorms, moire particularly to a counter-pressure method and apparatus for counteracting uplift pressures of hurricane-force winds.
The vast number of buildings now built in highly exposed regions and the apparently increasing frequency of category 4 and 5 hurricanes all portend more widespread destruction of houses and other buildings. Much of the destruction is needless. The loss of roofs in particular, with collateral damage to life and property can be preventable.
Many houses and other small buildings in the Caribbean and Central American xe2x80x9cHurricane Beltxe2x80x9d can lose their roofs to category 3 and 4 storms; much of such stock in the U.S. part of that Belt might be little better built. Several regions now require resistance to category 5 storms for new construction, and indeed it need not be unduly costly to incorporate such resistance during construction.
Engineers have established the efficacy of solidly shuttering windows and other weak openings in reducing wind uplift forces on roofs, and the limited but significant effect is quantified in today""s building codes (in stating worst-case uplift values for fully enclosed as against normally windowed small buildings). At least in the U.S.A., covering house windows with nailed on plywood sheets appears to be the favoured preparation in the face of an approaching hurricane, primarily to prevent glass breakage and wind and rain entry, but also to help thereby in keeping the roof from flying off. Such hurricane shutters are also described in more than a dozen U.S. patents, for example in U.S. Pat. No. 5,383,315 which is entitled HURRICANE SHUTTER REINFORCEMENT AND METHOD, issued to Birs on Jan. 24, 1995, and in U.S. Pat. No. 5,737,874 which is entitled SHUTTER CONSTRUCTION AND METHOD OF ASSEMBLY, issued to Sipos et al on Apr. 14, 1998.
Such storm-shuttering measures may be less commonly applied where most needed, such as on more modest houses, for elderly households or others lacking means and skills, and in much of the Caribbean or Central American parts of the Hurricane Belt where there are widespread inadequacies of the existing houses and small buildings. Plywood and its modern competitor OSB (Oriented Stand Board) are as close to ideal shuttering materials as any, but are still costly when used for the single job of protecting the glazing against missiles, to prevent breakage. In some cases the roof constructions are readily amenable to retro-reinforcing but often they are not. Both new construction and existing buildings are begging for lower cost means of xe2x80x9cadding strength just where neededxe2x80x9d.
Therefore, there is a need for providing a more efficient and less expensive method and apparatus for protecting buildings, particularly existing buildings, against hurricane force winds.
It is one object of the present invention to provide a method and apparatus for protecting roof structures against windstorms.
It is another object of the present invention to provide a method and apparatus to maintain indoor air pressure lower than the average outdoor pressure around a building to reduce a net uplift force on the roof of the building.
It is a further object of the present invention to provide a windstorm shutter functioning as a one-way valve to ensure a lower indoor air pressure of a building to counter the uplift forces on the roof.
It is a still further object of the present invention to provide a relatively inexpensive method and apparatus for protecting buildings against hurricanes.
In general terms there is a counter-pressure method for roof reinforcement against windstorms which comprises steps of providing a plurality of one-way venting valves over openings in a building envelope, respectively to ensure that at least one of the one-way venting valves is located on a lee side of the building envelope regardless of wind direction, the one-way venting valves closing under wind pressure to prevent inward air flow and being free to open to permit outward air flow when on the lee side; closing openings in the building envelope not covered by the one-way venting valves during windstorms; and whereby indoor air flows freely out of the building envelope through the at least one of the one-way venting valves to a lee zone on the lee side to depressurize the inside of the building envelope to counteract an uplifting force on a roof of the building envelope induced by winds over the roof.
The at least one venting passage is preferably sized to have a venting capacity larger than the total inward air leakage when the windows and other openings of the house are closed during windstorms. It is preferred that the venting passage comprises a one-way valve permitting outward air flow while preventing inward air flow so that the venting passage is closed only when the indoor air pressure is not higher that the pressure of the immediate outdoor area bounding the passage. And it is still preferred that the one-way valve venting passage is provided in a structure of the house at each side so that the venting passage toward a leeward area outdoors is open during windstorms.
In accordance with one embodiment of the present invention a counter-pressure method for protecting roofs against windstorms comprises a step of equipping storm shutters as the one-way valves placed over open windows to permit air flowing outwardly through or around the shutters while prevent air flowing inwardly so that the shutters on lee walls of the house are open while the windward shutters are closed during windstorms to maintain the indoor air pressure close to the lowest outdoor air pressure bounding the shutters. At least one such shutter is mounted on each face of the house so that at least one is subjected to a low pressure lee regardless of wind direction. In approaching storm conditions the shutters are mounted and the windows inboard of the one-way valve shutters are left open so that the indoor pressure will equalise quickly with the lee suction conditions during windstorms. Further, the glazing itself can be subjected to little or no load since air can pass freely through the open windows. The entire shutter can be used as a one-way valve, or one-way valves can be placed in the body of each shutter panel that is over an operable window, or the one-way valves can be placed around the perimeter of the shutter panel. Flexible polymeric materials make the design of the one-way valves clearly practical at low costs, in simple flap valve forms that can be retrofitted to existing storm shutters or incorporated in fabricating new shutters.
In accordance with another embodiment of the invention a counter-pressure method for protecting a roof against windstorms comprises a step of providing a plurality of the one-way valve passages on roof vents of the house which are in air communication with a space under the roof, to permit air flow from the space under the roof through one or more of the one-way valve passages to a leeward area outdoors while the remainder of the one-way valve passages are closed to prevent air from flowing inwardly therethrough into the space under the roof during windstorms.
In accordance with a further embodiment of the invention a counter-pressure method and apparatus for protecting a roof against windstorms are provided. A Venturi-tube is adapted to be installed in or on the house, vertically penetrating through the roof or positioned close alongside the roof, in such a manner that an open top of the Venturi-tube above the roof is subjected to winds blowing thereacross regardless of wind direction, and is in air communication with space under the roof so that a Venturi-action induced by winds blowing over the roof decrease air pressure in the space under the roof by xe2x80x9csuckingxe2x80x9d air out of the space through the Venturi-tube.
With respect to another aspect of the invention, there is provided a storm shutter having a panel adapted to be mounted over an opening in a structure of a house; and a valving mechanism attached to the panel for permitting outward air flow from an indoor area of the house through or around the panel to outdoors while preventing inward air flow so that the shutter works as a one-way valve to decrease air pressure of the indoor area to compensate for an uplift force on a roof of the house induced by windstorms when windows and other openings of the house are securely closed and an outdoor area bounding the shutter is in a lee zone of winds. The valving mechanism may include means for pivotally attaching one side of the panel to an outer surface of the structure and a stop member adapted to be associated between the panel and the structure to make the panel pivotable between a closed position for inhibiting inward air flow and an open position limited by the stop member for outward air flow. The valving mechanism may also be implemented with a flap member attached to an outer surface of the panel for selectively closing a porthole defined in the panel, or strip flap members around a perimeter of the panel for selectively closing a gap formed between an inner surface of the panel and an outer surface of the structure surrounding the opening so that inward air flow through the porthole or the gap is inhibited while outward air flow is permitted.
The methods and apparatus according to the invention ensure that indoor air pressure remains relatively negative during windstorms, that is, lower than the average outdoor pressure around a building, thus markedly reducing the net uplift force on the building""s roof. While the solid shuttering of windows and other glazed openings is itself known to help limit such uplift by limiting the amount of indoor over-pressure that winds can induce, this one-way valve-action and Venturi-action go radically further, inducing indoor xe2x80x9csuctionxe2x80x9d, relative to the ambient pressure outdoors.
Interpolating, for example from the xe2x80x9cworst casexe2x80x9d values given in ANSI-ASCE 7-95, the basis of leading building codes, one can infer that an un-shuttered example house may face peak uplifts across portions of its roof-ceiling of approximately 70 psf or more (in 130 mph hurricane winds), which would be reduced to about 50 psf or so with solid shuttering (a building with no openings) to prevent indoor over-pressure. The simple counter-pressure methods here presented can ensure negative indoor pressure, and negative pressure in the roof space where desirable, to keep the resultant uplift force down to perhaps 25 psf or less under the same conditions.